Hydroxyapatite (HAp, chemical formula Ca10(PO4)6(OH)2) has attracted the attention of researchers over the past thirty years as an implant material because of its excellent biocompatibility and bioactivity. HAp has been extensively used in medicine for implant fabrication. It is commonly the material of choice for the fabrication of dense and porous bioceramics. Its general uses include biocompatible phase-reinforcement in composites, coatings on metal implants and granular fill for direct incorporation into human tissue. It has also been extensively investigated for non-medical applications such as a packing material/support for column chromatography, gas sensors and catalysts, as a host material for lasers, and as a plant growth substrate.
Previously explored methods of hydroxyapatite synthesis for particles include plasma spraying, hydrothermal synthesis, freeze drying, sol-gel, phase transformation, mechanochemical synthesis, chemical precipitation, and precipitation in simulated body fluid (SBF). All of these methods produce products with varying levels of purity, size, crystallinity, and yield. Plasma spraying, hydrothermal synthesis, sol-gel, phase transformation, mechanochemical synthesis, and chemical precipitation require elevated temperatures and/or extreme pH values in the fabrication of hydroxyapatite. These conditions can raise important questions among biologists when considering the material for in vivo applications because they are not biomimetic and, in most cases, do not yield biomimetic structures or morphologies. Furthermore, precipitation in simulated body fluid has such a low yield or long reaction time, it is not practical for use in manufacturing implants.
Therefore, a need exists for hydroxyapatite synthesis to take place at room temperature and optional neutral pH to allow the exploration of synthesis with live cells, including those in living organisms.